Big See

2011 MDX, 60,000 miles. 2 weeks ago got a P0303 code (cylinder 3 misfire). Mechanic suggested replacing the coil -- code came back. Ran Seafoam through gas tank -- code came back. Replaced all the spark plugs with OEM plugs -- code came back. Opened up manifold and EGR ports looked fine but wiped it down and vacuumed it to be sure. Just put in more Seafoam and swapped the coil with another on the off-chance that the new coil is malfunctioning, but I expect the code to return. Running out of options - any suggestions before I take it in?

By the way about 2 weeks before this all started I was getting some engine knock even when I used top-tier premium so the dealership upgraded some software which made the knock go away -- could the misfire be related to this? Thanks for any and all help . . .

restron

go to an acura dealershiop

Big See

Thanks

VictorTL

Check your camshaft if bad replace it. Here this is what I did:
https://acurazine.com/forums/1g-2g-m...un-fun-968059/

Good luck!

Big See

Thank you!

thoiboi

Just to be sure, OEM coil? have you checked the 3rd cylinder wire harness that connects to the coil to see if maybe it's not frayed/cut/broken?

Big See

Yes, I replaced it with an OEM coil, and have also swapped the coils around. I did a quick look at the wire harness and it looked OK but I don't have the skill set to test the wires.

Funny thing is, after I erase the error code, it takes days for the code to return -- it seems like it would quickly come back if something was physically wrong (damaged wires/faulty fuel injector/valve issue). Car runs just fine. More and more I am thinking it has something to do with the software upgrade -- I read somewhere that a misfire can have something to do with the timing being off, and I read that to avoid engine knock the ECU can be programmed to adjust the timing, which is what I assume the Acura dealership did. At this point I am just waiting for the code to return so I can take it in to my mechanic with the active code. I will update this post with whatever permanent solution we come up with. Thanks for the response.

Big See

As promised, I am here to give the epilogue to the saga -- got it back from my mechanic yesterday and it was, as many people theorized, the fuel injector. In my 30 years of driving and multiple car ownerships, it's the first injector I've ever replaced. My mechanic told me he felt that Honda downgraded the design of their injectors by going to an all-plastic housing and that, while reliable, they are more prone to failure than Toyota and other brands. He said the injector was not clogged, but had an electrical failure. So hopefully this will help someone else with a persistent misfire on one cylinder.

thoiboi

sweet, thanks for the resolution!

VictorTL

Big See

No, the wire harness was good. Only problem was the fuel injector itself.